1. Related Applications
This application claims priority from GB 9416840.8, filed Aug. 19, 1994.
2. Field of the Invention
The present invention relates to a control system and method for a semi-automatic mechanical transmission system, including a manually operated shift selector, for automatically controlling the changing or shifting of transmission gear ratios on a vehicle, while leaving the vehicle driver or operator some residual measure of control. In particular, the present invention relates to a control system and method for the semi-automatic control of a mechanical change gear transmission including means for automatically executing automatically determined and displayed allowable driver selected transmission ratio shifts, including automatic control of the vehicle master clutch. A clutch pedal is provided and the master clutch operation is automated in all but start-from-stop situations. The clutch pedal is effective to override the automated clutch operator to cause disengagement of the master clutch. More particularly, the present invention relates to a system and method for controlling a semi-automatic mechanical transmission wherein, during automatic implementation of a downshift, if the master clutch is manually disengaged, the logic will only command a single attempt to engage the target ratio and, if substantially synchronous conditions for engaging the target ratio are not achieved, will thereafter discontinue attempts to achieve synchronous conditions to downshift the transmission by engine speed modulation until (i) the master clutch is sensed as engaged or (ii) the vehicle comes to rest.
3. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks and/or coaches, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith are well known in the prior art. Such fully automatic change gear transmissions include transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio and automated mechanical transmissions utilizing electronic, hydraulic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e., positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065; 4,361,060; 4,595,986; 5,050,079 and 5,109,729, the disclosures of which are incorporated herein by reference.
Many vehicle operators like to control the selection of the gear ratios, particularly since they can see and/or know the nature of the road ahead and/or of the load being carried. This requirement is satisfied by providing a semi-automatic mechanical transmission control wherein available gear ratios under existing operating conditions are displayed and automatic changing between a plurality of gear ratios is provided while normally permitting the driver to choose when to make a particular gear ratio change and whether to select the immediately consecutive ratio up or down or, by repetitive pulses in a given direction, to skip one or more ratios. Furthermore, the semi-automatic control system prohibits engagement of a driver selected higher ratio (i.e., an upshift) that would cause the engine speed to decrease below the idle speed (i.e., would cause stalling and/or over-stressing at low speeds of the engine) and of a lower ratio (i.e., a downshift) if such a change would cause over-speeding of the engine.
The semi-automatic transmission systems typically were provided with a non-manually controllable clutch actuator for controlling the master clutch during dynamic vehicle operation (usually above a predetermined ground speed) and a manually operated clutch pedal intended for start-from-stop operation and low-speed maneuvering.
Typically, the manual clutch control, usually a clutch pedal, was effective to override the non-manual actuator and cause master clutch disengagement, regardless of the position of the non-manual actuator, see European Pat. No. 0324553B1, the disclosure of which is incorporated herein by reference. Examples of the semi-automatic transmission systems and the controls therefor may be seen by reference to U.S. Pat. Nos. 4,648,290; 4,800,360; 4,930,081 and 4,930,078, the disclosures of which are incorporated herein by reference.
As is known in such systems, to allow engagement of a selected ratio, synchronous conditions must be established, i.e., input shaft speed must, within given limits, equal the product of output shaft speed multiplied by the target gear ratio (IS=OS * GR.sub.T). With the master clutch fully engaged (i.e., no slip), engine speed (ES) equals input shaft speed, and to achieve synchronous conditions, especially for a downshift, the fueling of the engine was manipulated, with the master clutch engaged, so that engine speed substantially equaled the product of output shaft speed multiplied by target gear ratio (ES=IS=OS * GR.sub.T). Upon achieving synchronous conditions, the positive jaw clutches associated with the target ratio were then engaged.
While the above-described semi-automatic mechanical transmission control does provide a very desirable semi-automatic control, the control was subject to improvement. In particular, in the prior art control, if the operator manually caused the master clutch to be disengaged during a downshift transient, the controller tended to repeatedly command acceleration of the engine in an attempt to cause synchronous conditions for engaging the target gear ratio. This resulted in rapid accelerations of the engine, which tended to be annoying as well as non-productive and wearing on the engine.